Some Points Concerning the Structure and Function of the Spleen

Abstract

1. The spleen is divided into segmental zones or lobes, corresponding to the branches of the arteria lienalis which enter it. These zones are at once arterial and nervous units. 2. The scheme of subdivision of the splenic nerve corresponds to these segmental zones, and stimulation of a branch of the nerve causes only a section of the spleen to contract. Central to the cæliac ganglion (e.g. in the splanchnic nerve or in the anterior spinal roots) there is no such segmental representation in the nerve branches proceeding to the spleen. 3. The splenic vein is conspicuously larger than the splenic artery, that of the ox having five times the diameter of the artery. When a short section of the vein is electrically stimulated it contracts and remains in strong contraction for an hour or more, the outflow of blood being greatly impeded. 4. When the spleen is perfused with Indian ink the particles may come to rest in four different situations: (1) in the ellipsoids ; (2) in the spleen phagocytes; (3) on the ordinary reticulum; (4) on the walls of the venous sinuses. 5. In the living animal deposition in the ellipsoids is temporary. Within three hours after intravenous injection of the ink, phagocytes have begun to clear the particles from the spaces within the ellipsoids. Twenty‐four hours later the ellipsoids are free. 6. The phagocytes of the pulp retain the particles for weeks on end. At first they clear the ink off the reticulum. After a month they are seen to have undergone a rearrangement, and some have migrated into the Malpighian corpuscles. 7. The ellipsoids act as valves, readily allowing the blood to flow in the normal direction, i.e. from the interior to the exterior of the ellipsoid, but instantly closing against higher pressure applied to their exterior. The existence of these valves accounts for the difficulty of perfusing the spleen backwards, i.e. from vein to artery. 8. Each ellipsoid is surrounded by a number of venous sinuses, which become dilated when the venous pressure is rased.

Development and function of the mammalian spleen

“…Given the presence of macrophages in these structures, and that erythrocytes and lymphocytes are able to migrate through these capillaries, it has been suspected that these vessels might have an immune function. They can trap particulate material from the blood, which can be ingested by the surrounding macrophages, (92,93) so they may be sites for clearance of blood-borne particles by phagocytosis. However, macrophages of the splenic marginal zone are still required for trapping of blood-borne particles in species such as mouse that do not have PAMS.…”

Branches of the splenic artery and splenic arterial segments

“…Segmentation of the spleen was later elaborated upon by other workers, including Tait and Cashin (1925), Dreyer and BudtzOlsen (1952), Braithwaite and Adams (1956), Clausen (1958), Gupta et al (1976), and Jit and Sahni (1991). There has been considerable difference regarding the number of vascular segments reported.…”

Some factors involved in the concentration of blood by the spleen

“…There are three possible explanations for this: (1) that corpuscles are manufactured in the spleen and added to the blood circulating through it, but all evidence is against the idea that the spleen in adult life manufactures corpuscles at all; (2) that the blood for some reason is held up in the spleen and during its sojourn the fluid is filtered off from it into spleen lymphatics, the corpuscles remaining in the pulp spaces. The samples then obtained by puncture of the pulp spaces will obviously be more concentrated than peripheral blood; (3) that the peculiar anatomical arrangement of the vascular bed in the spleen may favour a form of plasma skimming whereby corpuscles are concentrated through removal of plasma by the blood stream.…”